The present invention relates to a technique for judging a cylinder corresponding to each stroke of combustion cycle based on cylinder judgment signals output from a cam sensor in a vehicle engine, and particularly relates to a technique for coping with a problem at fault time of the cam sensor.
An earlier vehicle engine is equipped with a cylinder judgment apparatus for judging a cylinder corresponding to each stroke of combustion cycle for controlling fuel injection timing and ignition timing for each cylinder.
In a cylinder judgment apparatus disclosed in Japanese Unexamined Patent publication No. 5-106500, cylinder judgment signals corresponding to the number of cylinders are output from a cam sensor during a time period between outputs of reference crank angle signals from a crank angle sensor, to perform cylinder judgment.
However, in a multi-cylinder engine, for example, a six-cylinder engine, since a signal plate for outputting cylinder judgment signals needs to be provided with a maximum of six units to be detected during the time between the outputs of the reference crank angle signals, there is a problem in that the signal plate cannot be miniaturized, especially in a construction where a magnetic sensor is used to detect projections formed thereon.
The present invention has an object of providing a cylinder judgment apparatus and a cylinder judgment method of an engine, capable of performing cylinder judgment based on only signals from a cam sensor and also detecting erroneous judgment due to noise mixing, thereby improving reliability.
In order to achieve the above object, the present invention is constructed to include a plurality of cam sensors each of which outputs cylinder judgment signals for judging a cylinder corresponding to each stroke of combustion cycle for each uneven interval of a crank angle and to perform cylinder judgment by a control unit as follows.
The number of cylinder judgment signals output from one cam sensor during a time period between a previous output and a present output of cylinder judgment signals from the other cam sensor is counted up and a specific cylinder is judged based on the number of outputs, so that the cylinders other than the specific cylinder are judged based on the judgment result and the cylinder judgment signals.
On the other hand, each time the cylinder is judged by the above method, a period of from the previous cylinder judgment to the present cylinder judgment is calculated and erroneous detection of cylinder judgment signal due to noise is judged based on a ratio between a previous calculation value and a present calculation value of the period.
When the erroneous detection is judged, a cylinder judgment result based on the cylinder judgment signals is cancelled.
The other objects and features of the present invention will become understood from the following description with the accompanying drawings.